NU Ori is a massive spectroscopic and visual binary in the Orion Nebula Cluster , with 4 components : Aa , Ab , B , and C. The B0.5 primary ( Aa ) is one of the most massive B-type stars reported to host a magnetic field .
We report the detection of a spectroscopic contribution from the C component in high-resolution ESPaDOnS spectra , which is also detected in a Very Large Telescope Interferometer ( VLTI ) dataset .
Radial velocity ( RV ) measurements of the inner binary ( designated Aab ) yield an orbital period of 14.3027 ( 7 ) d. The orbit of the third component ( designated C ) was constrained using both RVs and interferometry .
We find C to be on a mildly eccentric 476 ( 1 ) d orbit .
Thanks to spectral disentangling of mean line profiles obtained via least-squares deconvolution we show that the Zeeman Stokes V signature is clearly associated with C , rather than Aa as previously assumed .
The physical parameters of the stars were constrained using both orbital and evolutionary models , yielding M _ { Aa } = 14.9 \pm 0.5 M _ { \odot } , M _ { Ab } = 3.9 \pm 0.7 M _ { \odot } , and M _ { C } = 7.8 \pm 0.7 M _ { \odot } .
The rotational period obtained from longitudinal magnetic field \langle B _ { z } \rangle measurements is P _ { rot } = 1.09468 ( 7 ) d , consistent with previous results .
Modeling of \langle B _ { z } \rangle indicates a surface dipole magnetic field strength of \sim 8 kG .
NU Ori C has a magnetic field strength , rotational velocity , and luminosity similar to many other stars exhibiting magnetospheric H \alpha emission , and we find marginal evidence of emission at the expected level ( \sim 1 % of the continuum ) .